Field of the Invention
The invention relates to a cylinder head for a piston compressor having an intake valve, a pressure valve and an unloader, wherein a ring-shaped intake chamber arranged on the inside or outside radially and a pressure chamber situated on the inside radially or on the outside radially are provided in the cylinder head, a unloader ring having a number of lifting fingers passing through the intake channels of the intake valve is arranged in the ring-shaped intake chamber, so that the unloader ring is guided displaceably on the wall of the intake chamber by the circumferential surface of the unloader ring on the outside radially or by the circumferential surface of the unloader ring on the inside radially, a radial step being provided on the circumferential surface of the unloader ring on the outside radially or on the circumferential surface of the unloader ring on the inside radially, and a control chamber which communicates with a control line for supplying a control medium into the control chamber is formed on the circumferential surface of the unloader ring on the outside radially or on the circumferential surface of the unloader ring on the inside radially, with a control chamber formed between the wall of the intake channel and the radial step connected to a control line for supplying a control medium into the control chamber.
The Prior Art
In many applications, high demands are made of the design height of a compressor in air brake compressors, e.g., for trucks. Likewise, idling control must often be provided with compressors, in particular compressors, which are driven even if no compression medium such as air is required at that time. An unloader is frequently used with many compressors, forcing the intake valve to remain open for a certain period of time. However, there are no known air brake compressors that use unloaders, and instead other devices are also used, e.g., pistons or movable slats, which open a borehole, or intake vanes, which are shifted. The unloader or the actuating device for same is therefore often situated on the cylinder head and has unloader fingers which are pressed against the valve element of the intake valve to lift it away from the valve seat and thus to keep it open. However, such unloaders according to the related art require a very large installation space, which therefore prevents their use in many applications. One such unloader is known from EP 475 931 A1 or EP 118 416 A1, for example.
U.S. Pat. No. 2,956,729 A in turn describes an unloader situated concentrically around the cylinder of the compressor. To do so, a ring-shaped step piston, which is in contact with a number of pins that are distributed over the circumference and extend through the intake channels in the valve seal and actuate the pins, is provided. A hollow space, which can be put under pressure via a hydraulic medium line may be placed between the movable step piston and the stationary inside part, so that the unloader is deactivated. To actuate the unloader, the intermediate space must be vented, so that the unloader keeps the intake valve open by spring force. One such unloader has a plurality of individual parts which makes it susceptible to error. The pins must also be guided in the valve seat, which reduces the available intake cross section by the intake valve on the one hand while limiting the possible number of pins on the other hand. In the case of a few pins, however, the surface pressure of the pins on the valve plate is increased, resulting in unwanted deformation, in particular warping of same, and thus resulting in a malfunction of the compressor.
U.S. Pat. No. 1,345,884 A shows an unloader having lifting pins situated in the cylinder head. The lifting pins are pressure-actuated directly, so that corresponding channels for the pressure medium must be provided in the cylinder head. This makes the cylinder head complicated and reduces the available flow cross sections for the pressure medium or the intake medium. Here again, the pins must be guided in the valve seat of the intake valve, which in turn reduces the available intake cross section due to the intake valve and limits the possible number of pins, with the same disadvantages as those described in U.S. Pat. No. 2,956,729 A.
FR 2 257 029 A1 describes a cylinder head of a piston compressor in which a unloader ring according to the preamble of the independent claim is derived. In normal operation, the unloader ring is lifted away from the valve element by a control medium against a spring. In the absence of a control pressure, the unloader ring is pressed by the spring against the valve element, lifting it away from the valve seat.
In idling operation, oil is transported from the crankcase into the cylinder chamber (the so-called oil carry-over). This has negative effects en the operation of the compressor because on the one hand the oil is transported outward and delivered to the environment and on the ether hand there may also be some chemical decomposition of the oil due to the high temperatures of the compression medium and/or of the cylinder head, such that the resulting substances may be problematical for units downstream from the compressor, for example, control valves for a brake system and may cause damages there.
The object of the present invention is therefore to provide a very compact cylinder head with unloaders which will eliminate the aforementioned disadvantages and will reduce the oil carry-over in idling operation.